I would like to help a friend's daughter switch out an existing 20g planted tank with gravel substrate to a soil substrate, but have some concerns about whether it's possible to do without harming the existing fish inhabitants (currently 3 gold tetras, 2 rummynoses, 1 neon).

It's been a while since I've set up a Walstad style tank, so I pulled out my copy of The Ecology of a Planted Aquarium and have been doing some revisiting of chapters, especially on the soil she uses and when she adds in fish. According to Ms. Walstad, she would add fish the very next day after setting up the soil substrate, using regular potting soil without added fertilizers.

She also discusses adding soil to an existing tank without draining the water by adding chunks of soil in wax paper, taped with scotch tape and then inserting these packages of soil under the gravel. Once under the gravel, she suggests punching holes into the packages to speed up the process.

So, I'm wondering if we can do this by following these steps, using regular potting soil w/out ferts:

1. drain as much of the tank water and reserve, net fish and place into holding bucket with heater and airstone

2. place soil bricks under gravel, add a bit new gravel (pre-rinsed) to appropriate 2" depth.

3. fill tank with new water and drain

4. fill tank with saved old tank water

5. run tank for 1-2 hours? to cycle through filter, and bring up to appropriate temp, add Stability water conditioner

It would be easier to remove everything including substrate then add dirt, soak with water, add layer of old substrate, plants, water, filter, fish and you're good to go.

That's true, for some reason I was thinking wrapping the dirt might make it less toxic for reintroducing the fish immediately.... but is that not a concern? Could we just add the fish back in after filling and draining the tank once?

It appears that I may be able to use MGOCPM instead of regular top soil for this. Can anyone answer if they've done this that it is ok to add the fish back in immediately if using capped Miracle Grow Organic soil w/ a seeded filter and saved aquarium water?

It appears that I may be able to use MGOCPM instead of regular top soil for this. Can anyone answer if they've done this that it is ok to add the fish back in immediately if using capped Miracle Grow Organic soil w/ a seeded filter and saved aquarium water?

I have MGOCPM capped with sand in a tank that I am cycling right now, along with a seeded filter from another tank. I have had around 100 mosquito fish in the tank ever since filling it and they are doing fine. All of the water parameters seem to be stable, although I had a small ammonia spike after first adding the fish. I am planning a cichlid tank, but am using the mosquitofish for cycling. I probably wouldnt drop any expensive or cherished fish in the tank for a week or two just to be safe. I'm sure the MGOCPM has stuff in it that I can't check with a generic water test kit.

Thanks Indychus. With the seeded filter and aquarium water, I believe we'll avoid any ammonia spike; however, I am worried about whether there is anything in the MGOCPM that could potentially leach toxins.

From what I've been reading today though it appears many people are adding fish immediately after the water clears, either same day or the next. So, I think all should be ok. We'll plan to sift through and pick out any large pieces of bark from the soil.

We're planning to add a school of neons, and a trio of cories too, but will wait on those until certain about water parameters.

Hopefully this goes well Her family is going through some changes right now and I'd like to help her with this as a bit of positive light for her during this time.

Read the thread this morning but had to get a break at work to reply.
Below is a short thread on a single day swap from a 20g long to a 29g adding MGOCPM. Timeline and pics on how I handled the swap.
No losses to date playing with the bagged dirt.Another NPT or D's Dirt Tank

Read the thread this morning but had to get a break at work to reply.
Below is a short thread on a single day swap from a 20g long to a 29g adding MGOCPM. Timeline and pics on how I handled the swap.
No losses to date playing with the bagged dirt.Another NPT or D's Dirt Tank

HTH

Thank you, just the confirmation I needed!

Question on the prep of the MGOCPM.... did you sift out large bark pieces and did you wet it, prior to adding it to the tank?

When setting up the first time, you do screen out large pieces then. Have you ever added fish immediately after using fresh MGOCPM?

Don't screen it, if you see a big offending chunk of something remove it.
Put in about a 1 or 1.5" layer of it dry. Press your hand down on it to gage depth. With gravel you need a thicker cap because the pebbles don't seal well, probably 2" or add some pool filter sand along with the gravel to aid in sealing the cap. Add enough water to cover the layers then press the flat palm of you hand down on it patting to aid air release then continue with the fill. 19/20 tanks never had a hiccup adding critters right away but I don't use gravel.

I converted a 29G this way and it worked like a charm. Below are the steps I took:

1. Remove old tank water, fish, decorations, etc.
2. Don't forget to keep the filter running in tank water (even if it's a 5g bucket).
3. Clean tank
4. Add 2 inches of dirt and compact it with your hands
5. Add 1 inch of sand as a cap. I found that sand works better in keeping the dirt in place and allowing plants to root. Gravel makes it harder for plants to root.
6. Plant the plants
7. Add old tank water, slowly.
8. Let the filter ran for a few hours in the tank.
9. Add Prime for good measure (just in case)
10. Reintroduce fish

I am in the process of doing what you are contemplating. I had the same questions that you did prior to starting but did not get a satisfactory definitive answer to the safety of the fish upon reintroduction.

I incurred an ammonia spike that lasted 24 hours and now in day 7 of the process, nitrites have been stubborn at .25 ppm. They peaked at .5 ppm and dropped quickly but has not zeroed out. I will not introduce my fish until two consecutive days of zero ammonia and nitrites.

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